It sounds like he’s moving to America, not just going for a holiday. I’m sure he’d think it was pretty great if you kiss him goodbye the last time you see him. But remember you’re only 11, so a quick peck on the cheek is all that’s required. There will be plenty of time for kissing when you are older. For now, just let him know you’ve enjoyed his company and you hope he has a really great life in America. Maybe you’ll catch up again when you’re both adults.
But if he is actually only going for a holiday, I don’t think you should kiss him. When he comes back, he might expect it to continue, and that’s not a good look for a pre-teen.